(1) Field of the Invention
The present invention relates to a method and an apparatus for controlling fuel injection for an internal combustion engine, more particularly to a fuel injection control method for internal combustion engine in which the fuel injection is carried out asynchronously with the rotation of a crank shaft at the acceleration time so as to improve the acceleration response, and an apparatus for realizing the method.
(2) Conventionally, in an electronically controlled fuel injection unit for regulating the fuel amount to be injected from a fuel injection valve depending on operating conditions for the internal combustion engine, calculation for the fuel injection amount and control of the fuel injection were performed in accordance with a signal corresponding to the crank angle, which is produced in synchronization with the rotations of the crank shaft.
FIG. 1 shows a timing chart of the fuel injection in which the X axis indicates the time elapsed while the Y axis indicates a throttle valve opening TA and intake air flow Q per one revolution of the engine with the engine speed being constant at 1000 rpm and the change in the intake air flow Q and are shown as correlational characteristics. That is, in FIG. 1, according to the conventional method for satisfying the output required for the engine, the fuel injection amount was calculated in accordance with the intake air flow and the engine speed at the timing of T.sub.1 through T.sub.3 in synchronization with the rotations of the crank shaft at every crank angle (hereinafter referred to as CA) of 360.degree. (deg.) and the fuel injection was carried out just after the calculation or at the subsequent time period synchronized with the crank signal at every 180.degree. of CA.
For these reasons, acceleration is started just after the calculation of the fuel injection amount at the timing T.sub.2 in FIG. 1 and when the intake air flow Q changes rapidly, the fuel injection amount shown by .tau..sub.2 is to be insufficient to the actual intake air flow Q. As a result, there is a problem that any cylinder will be in a "lean" condition in the air/fuel ratio and this results in a burning and the engine will be in a so-called "breathed condition", with the result that the acceleration response becomes not good.
In order to improve the problem mentioned above, a method and apparatus for performing fuel injection control has been proposed heretofore in which stamping on or the operation of the accelerator, i.e. the accelerating operation is detected by use of an idle switch and a constant amount of fuel is injected asynchronously with the rotation of the crank shaft. However, the necessary amount for fuel to be injected is largely changed in accordance with the output required, the engine speed, the speed of the operation of the accelerator (variable in the throttle valve opening per unit time), or accelerated conditions of a load when starting acceleration. On the other hand, either excess or shortage of the fuel injection occurs for the required output when the asynchronous fuel injection of the constant amount mentioned above is to be carried out, so that a suitable fuel injection remains unsolved.
Moreover, when the engine speed having a sufficient acceleration response is relatively high without performing the asynchronous fuel injection mentioned above or when the engine is halted at the engine start or it is in a low rotational zone, the operation of the accelerator causes unnecessary fuel to be injected, to that the air/fuel ratio becomes excessively "rich", thus remaining the problems such as degradation of exhaust gas emission and a factor or cause of an unfavorable engine start unsolved.